The inertance hydraulic converter is an energy-efficient hydraulic component, its output efficiency and dynamic performance are seriously affected by the switched valve. This paper proposed an innovative a rotary inertance hydraulic converter (RIHC), which uses a continuous controlling turntable to determine the ratio of the high pressure oil and the low pressure oil to change the output energy, instead of the discrete controlling of the switched valve. The working principle and mechanical design of the RIHC are described, and mathematical models are established. The effects of the key variables on energy efficiency are evaluated using numerical analysis. The operating performance is analyzed based on simulation, and a control strategy to achieve stable system output is proposed. The results provide a foundation for theoretical research and practical application of the novel RIHC.